In order to ensure a good closing contact, possible adjustment means for the valve seat have already been proposed. In WO97/09555 it is proposed to provide the valve seat on a tube which is displaceably inserted in a bore in the housing and is for example glued after adjustment relative to the sealing surface. Thus in the case of this type of adjustment it is ensured that in closing contact the sealing surface comes into contact with the valve seat.
By the use of correspondingly soft seal it is possible to compensate for further manufacturing tolerances in order to achieve a tight closure of the valve seat in the closed position. However, if setting members are used which only have a relatively small travel of for example 1/10 to 2/10 mm, the seals must be of substantially harder construction in order to free the valve seat to a sufficient extent in the open position. Also in the case of such a construction of the valve in order to achieve a tight closure of the valve in the closed position, the valve seat and the sealing surface must be aligned with one another as well as possible.